Microelectric contact structure

ABSTRACT

Spring contact elements are fabricated by depositing at least one layer of metallic material into openings defined on a sacrificial substrate. The openings may be within the surface of the substrate, or in one or more layers deposited on the surface of the sacrificial substrate. Each spring contact element has a base end portion, a contact end portion, and a central body portion. The contact end portion is offset in the z-axis (at a different height) than the central body portion. The base end portion is preferably offset in an opposite direction along the z-axis from the central body portion. In this manner, a plurality of spring contact elements are fabricated in a prescribed spatial relationship with one another on the sacrificial substrate. The spring contact elements are suitably mounted by their base end portions to corresponding terminals on an electronic component, such as a space transformer or a semiconductor device, whereupon the sacrificial substrate is removed so that the contact ends of the spring contact elements extend above the surface of the electronic component. In an exemplary use, the spring contact elements are thereby disposed on a space transformer component of a probe card assembly so that their contact ends effect pressure connections to corresponding terminals on another electronic component, for the purpose of probing the electronic component.

REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is a continuation-in-part ofcommonly-owned, copending U.S. patent application Ser. No. 60/034,053filed Dec. 31, 1996, which is incorporated by reference herein.

[0002] This patent application is also a continuation-in-part ofcommonly-owned, copending U.S. patent application Ser. No. 08/452,255(hereinafter “PARENT CASE”) filed May 26, 1995 and its counterpart/PCTpatent application Ser. No. PCT/US95/14909 filed Nov. 13, 1995, both ofwhich are continuations-in-part of commonly-owned, copending U.S. patentapplication Ser. No. 08/340,144 filed Nov. 15, 1994 and its counterpartPCT patent application number PCT/US94/13373 filed Nov. 16, 1994, bothof which are continuations-in-part of commonly-owned, U.S. patentapplication Ser. No. 08/152,812 filed Nov. 16, 1993 (now U.S. Pat. No.5,476,211, Dec. 19, 1995), all of which are incorporated by referenceherein.

[0003] This patent application is also a continuation-in-part of thefollowing commonly-owned, copending U.S. patent application Ser. Nos.:

[0004] 08/526,246 filed Sep. 21, 1995 (PCT/US95/14843, Nov. 13, 1995);

[0005] 08/533,584 filed Oct. 18, 1995 (PCT/US95/14842, Nov. 13, 1995);

[0006] 08/554,902 filed Nov. 9, 1995 (PCT/US95/14844, Nov. 13, 1995);

[0007] 08/558,332 filed Nov. 15, 1995 (PCT/US95/14885, Nov. 13, 1995);

[0008] 08/602,179 filed Feb. 15, 1996 (PCT/US96/08328, May 28, 1996);

[0009] 60/012,027 filed Feb. 21, 1996 (PCT/US96/08117, May 24, 1996);

[0010] 60/005,189 filed May 17, 1996 (PCT/US96/08107, May 24, 1996); and

[0011] 60/024,555 filed Aug. 26, 1996,

[0012] all of which (other than the provisional patent applications)arecontinuations-in-part of the aforementioned PARENT CASE, and all ofwhich are incorporated by reference herein.

TECHNICAL FIELD OF THE INVENTION

[0013] The present invention relates to resilient electrical contact(interconnection) elements (structures) , also referred to as springcontacts, suitable for effecting pressure connections between electroniccomponents and, more particularly, to microminiature spring contactssuch as may be used in probing (resiliently and temporarily contacting)microelectronic components such as active semiconductor devices.

BACKGROUND OF THE INVENTION

[0014] Commonly-owned U.S. patent application Ser. No. 08/152,812 filedNov. 16. 1993 (now U.S. Pat. No. 4,576,211, issued Dec. 19, 1995), andits counterpart commonly-owned copending “divisional” U.S. patentapplications Ser. Nos. 08/457,479 filed Jun. 1, 1995 (status: pending)and 08/570,230 filed Dec. 11, 1995 (status: pending), all by KHANDROS,disclose methods for making resilient interconnection elements formicroelectronics applications involving mounting an end of a flexibleelongate core element (e.g., wire “stem” or “skeleton”) to a terminal onan electronic component coating the flexible core element and adjacentsurface of the terminal with a “shell” of one or more materials having apredetermined combination of thickness, yield strength and elasticmodulus to ensure predetermined force-to-deflection characteristics ofthe resulting spring contacts. Exemplary materials for the core elementinclude gold. Exemplary materials for the coating include nickel and itsalloys. The resulting spring contact element is suitably used to effectpressure, or demountable, connections between two or more electroniccomponents, including semiconductor devices.

[0015] Commonly-owned, copending U.S. patent application Ser. No.08/340,144 filed Nov. 15, 1994 and its corresponding PCT patentapplication Ser. No. PCT/US94/13373 filed Nov. 16, 1994 (WO95/14314,published May 26, 1995), both by KHANDROS and MATHIEU, disclose a numberof applications for the aforementioned spring contact element, and alsodisclosed techniques for fabricating contact pads at the ends of thespring contact elements. For example, in FIG. 14 thereof, a plurality ofnegative projections or holes, which may be in the form of invertedpyramids ending in apexes, are formed in the surface of a sacrificiallayer (substrate) . These holes are then filled with a contact structurecomprising layers of material such as gold or rhodium and nickel. Aflexible elongate element is mounted to the resulting contact structureand can be overcoated in the manner described hereinabove. In a finalstep, the sacrificial substrate is removed. The resulting spring contacthas a contact pad having controlled geometry (e.g., sharp points) at itsfree end.

[0016] Commonly-owned, copending U.S. patent application Ser. No.08/452,255 filed May 26, 1995 and its corresponding PCT patentapplication Ser. No. PCT/US95/14909 filed Nov. 13, 1995 (WO96/17278,published Jun. 6, 1996), both by ELDRIDGE, GRUBE, KHANDROS and MATHIEU,disclose additional techniques and metallurgies for fabricating contacttip structures on sacrificial substrates, as well as techniques fortransferring a plurality of spring contact elements mounted thereto, enmasse, to terminals of an electronic component (see, e.g., FIGS. 11A-11Fand 12A-12C therein).

[0017] Commonly-owned, copending U.S. Provisional Patent Application No.60/005,189 filed May 17, 1996 and its corresponding PCT patentapplication Ser. No. PCT/US96/08107 filed May 24, 1996 (W096/37332,published Nov. 28, 1996), both by ELDRIDGE, KHANDROS, and MATHIEU,discloses techniques whereby a plurality of contact tip structures (see,e.g, #620 in FIG. 6B therein) are joined to a corresponding plurality ofelongate contact elements (see, e.g., #632 of FIG. 6D therein) which arealready mounted to an electronic component (#630). This patentapplication also discloses, for example in FIGS. 7A-7E therein,techniques for fabricating “elongate” contact tip structures in the formof cantilevers. The cantilever tip structures can be tapered, betweenone end thereof and an opposite end thereof. The cantilever tipstructures of this patent application are suitable for mounting toalready-existing (i.e., previously fabricated) raised interconnectionelements (see, e.g., #730 in FIG. 7F) extending (e.g., free-standing)from corresponding terminals of an electronic component (see. e.g., #734in FIG. 7F).

[0018] Commonly-owned, copending U.S. Provisional Patent Application No.60/024,555 filed Aug. 26, 1996, by ELDRIDGE, KHANDROS and MATHIEU,discloses, for example at FIGS. 2A-2C thereof, a technique whereby aplurality of elongate tip structures having different lengths than oneanother can be arranged so that their outer ends are disposed at agreater pitch than their inner ends. Their inner, “contact” ends may becollinear with one another, for effecting connections to electroniccomponents having terminals disposed along a line, such as a centerlineof the component.

[0019] The present invention addresses and is particularly well-suitedto making interconnections to modern microelectronic devices havingtheir terminals (bond pads) disposed at a fine-pitch. As used herein,the term “fine-pitch” refers to microelectronic devices that have theirterminals disposed at a spacing of less than 5 mils, such as 2.5 mils or65 μm. As will be evident from the description that follows, this ispreferably achieved by taking advantage of the close tolerances thatreadily can be realized by using lithographic rather than mechanicaltechniques to fabricate the contact elements.

SUMMARY OF THE INVENTION

[0020] An object of the present invention is to provide an improvedtechnique for fabricating spring contact elements.

[0021] Another object of the invention is to provide a technique forfabricating spring contact elements using processes that are inherentlywell-suited to the fine-pitch close-tolerance world of microelectronics.

[0022] Another object of the invention is to provide a technique forfabricating spring contact elements that are suitable for probingelectronic components such as semiconductor devices, and that is readilyscaleable to probing fine-pitch peripheral interconnect structures.

[0023] Another object of the invention is to provide a technique forfabricating spring contact elements that are suitable for socketingelectronic components such as semiconductor devices, such as forperforming burn-in on said devices.

[0024] According to the invention, an elongate spring contact elementsuitable for microelectronic applications is fabricated by formingdepressions (such as trenches, such as by etching) in a sacrificialsubstrate and depositing (such as by plating) metallic materials intothe depressions. A plurality of spring contact elements may befabricated in this manner on a single sacrificial substrate, withlithographically-defined tolerances (e.g., dimensions, spacings).

[0025] The resulting spring contact elements may then be mounted toanother substrate such as a passive substrate or an active substratesuch as a semiconductor device, after which the sacrificial substrate isremoved.

[0026] An exemplary spring contact element formed in this manner has alength “L” between its base end and its contact end. The base end ispreferably offset in a first direction from a central portion of thespring contact element, and the contact end is preferably offset in anopposite direction from the central portion. In this manner, the overallspring contact element is not planar and, when its base end is mountedto an electronic component, its contact end extends above the surface ofthe electronic component to which it is mounted.

[0027] An exemplary sacrificial substrate upon which the spring contactelements may be fabricated is a silicon wafer, in which case the processof the present invention advantageously utilizes the directionallyselective etching of silicon used for micro-machining processes tocreate an electroform which is used to plate up the final spring contactelement. This approach may optionally employ laser-based ablation ofphotoresist, as opposed to lithographic development of the photoresist,in order to create the high aspect ratio of width to height which isrequired for fine pitch spacings between the spring contact elements.

[0028] An exemplary application for the spring contact elements of thepresent invention is as probe elements used to effect pressureconnections between a substrate and a device-under-test (DUT), in whichcase the spring contact elements are suitably mounted to a spacetransformer component of a probe card assembly, such as is described inthe aforementioned 08/554,902 and PCT/US95/14844. Alternatively, thespring contact elements are mounted to and extend from an activeelectronic component such as an application specific integrated circuit(ASIC).

[0029] The spring contact element is suitably formed of at least onelayer of a metallic material selected for its ability to cause theresulting contact structure to function, in use, as a spring (i.e.,exhibit elastic deformation) when force is applied to its contact (free)end.

[0030] The resulting spring contact element is preferably “long andlow”, having:

[0031] a length “L”, as measured from one end to another end;

[0032] a height “H” measured transverse the length in a direction thatis normal (z-axis) to the surface of the sacrificial substrate (and,normal to the component to which the spring contact element isultimately mounted);

[0033] a contact end portion which is offset in a one direction (e.g.,negative along the z-axis) from a central portion of the spring elementby a distance “d1”; and

[0034] a base end portion which is offset in one direction (e.g.,positive z-axis) from the central portion of the spring element by adistance “d2”.

[0035] The spring contact element is preferably tapered from the one(base) end to the other (contact) end thereof, the spring contactelement having the following dimensions:

[0036] a width “w1” at its base end as measured parallel to the surfaceof the sacrificial substrate and transverse to the longitudinal axis ofthe spring element;

[0037] a width “w2” at its contact end as measured parallel to thesurface of the sacrificial substrate and transverse to the longitudinalaxis of the spring element;

[0038] a thickness “t1” at its base end, measured along the z-axis; and

[0039] a thickness “t2” at its contact end, measured along the z-axis;resulting in:

[0040] a widthwise taper angle “α” (alpha); and

[0041] a thickness taper angle “β” (beta).

[0042] The spring contact element is also suitably provided with aprojecting feature at its contact end, said feature having a dimension“d3” measured along the z-axis.

[0043] There is thus described herein an exemplary spring contactelement suitable for effecting connections between two electroniccomponents, typically being mounted by its base end to a one of the twoelectronic components and effecting a pressure connection with itscontact end (e.g., by the projecting feature) to an other of the twoelectronic components, having the following dimensions (in mils, unlessotherwise specified): dimension range preferred L  10-1000  60-100 H4-40  5-12 d1 3-15 7 ± 1 d2 0-15 7 ± 1 d3 0.25-5    3 w1 3-20  8-12 w21-10 2-8 t1 1-10 2-5 t2 1-10 1-5 α  0-30°  2-6° β  0-30°  0-6°

[0044] Other objects, features and advantages of the invention willbecome apparent in light of the following description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Reference will be made in detail to preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. The drawings are intended to be illustrative, not limiting.

[0046] Although the invention will be described in the context of thesepreferred embodiments, it should be understood that it is not intendedto limit the spirit and scope of the invention to these particularembodiments.

[0047] Certain elements in selected ones of the drawings are illustratednot-to-scale, for illustrative clarity.

[0048] Often, similar elements throughout the drawings are referred toby similar references numerals. For example, the element 199 may besimilar in many respects to the element 299 in another figure. Also,often, similar elements are referred to with similar numbers in a singledrawing. For example, a plurality of elements 199 may be referred to as199 a, 199 b, 199 c, etc.

[0049]FIG. 1A is a cross-sectional view of a spring contact element,according to the invention.

[0050]FIG. 1B is a plan view of the spring contact element of FIG. 1A,according to the invention.

[0051]FIG. 1C is a cross-sectional view of an alternate embodiment of aspring contact element, according to the invention.

[0052]FIG. 1D is an enlarged cross-sectional view of the spring contactelement of FIG. 1C.

[0053]FIG. 1E is a cross-sectional view of an alternate embodiment of aspring contact element, according to the invention.

[0054] FIGS. 2A-2I are cross-sectional views of a technique forfabricating spring contact elements on a sacrificial substrate,according to the invention.

[0055]FIG. 2J is a cross-sectional view of a spring contact elementresiding on a sacrificial substrate, according to the invention.

[0056]FIG. 3A is a cross-sectional view of an alternate embodiment of aspring contact element residing on a sacrificial substrate, according tothe invention.

[0057]FIG. 3B is a perspective view of the spring contact element ofFIG. 3A, omitting a showing of the sacrificial substrate, according tothe invention.

[0058] FIGS. 4A-4B are cross-sectional views illustrating a techniquefor mounting a plurality of spring contact elements which initially areresident on a sacrificial substrate to another component such as a spacetransformer, according to the invention.

[0059]FIG. 4C is a cross-sectional view of a plurality of spring contactelements mounted to a component such as a space transformer, in use,probing (making temporary pressure connections with) another componentsuch as a semiconductor device, according to the invention.

[0060]FIG. 4D is a cross-sectional view of another embodiment (compareFIG. 4B) of a technique for mounting a plurality of spring contactelements to another component such as a space transformer, according tothe invention.

[0061]FIG. 4E is a cross-sectional view of another embodiment (compareFIG. 4B) of a technique for mounting a plurality of spring contactelements to another component such as a space transformer, according tothe invention. This figure also illustrates another embodiment of aspring contact element, according to the invention.

[0062]FIG. 4F is a cross-sectional view of another embodiment (compareFIG. 4E) of a technique for mounting a plurality of spring contactelements to another component such as a space transformer, according tothe invention. This figure also illustrates another embodiment of aspring contact element, according to the invention.

[0063]FIG. 5 is a schematic (stylized) plan view illustration of anapplication (use) for the spring contact elements of the presentinvention.

[0064]FIG. 6 is a schematic (stylized) plan view illustration of anotherapplication (use) for the spring contact elements of the presentinvention.

[0065]FIG. 7A is a cross-sectional view of another embodiment (compareFIG. 4D) of a technique for mounting a spring contact element to anothercomponent such as a space transformer, according to the invention.

[0066]FIG. 7B is a cross-sectional view of another embodiment (compareFIG. 7A) of a technique for mounting a spring contact element to anothercomponent such as a space transformer, according to the invention.

[0067]FIG. 7C is a cross-sectional view of another embodiment (compareFIG. 7A) of a technique for mounting a spring contact element to anothercomponent such as a space transformer, according to the invention.

[0068]FIG. 7D is a cross-sectional view of another embodiment (compareFIG. 7A) of a technique for mounting a spring contact element to anothercomponent such as a space transformer, according to the invention.

[0069]FIG. 8A is a perspective view of an alternate embodiment of aspring contact element (compare FIG. 3B), omitting a showing of thesacrificial substrate, according to the invention.

[0070]FIG. 8B is a perspective view of an alternate embodiment of aspring contact element (compare FIG. 8A), omitting a showing of thesacrificial substrate, according to the invention.

[0071]FIG. 9A is a side cross-sectional view of a first step in atechnique for achieving controlled impedance in a spring contactelement, according to the invention.

[0072]FIG. 9B is a side cross-sectional view of a next step in thetechnique for achieving controlled impedance in a spring contactelement, according to the invention.

[0073]FIG. 9C is an end cross-sectional view of t he controlledimpedance spring contact element of FIG. 9B, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0074] Commonly-owned, copending U.S. patent application Ser. No.08/554,902 filed Nov. 9, 1995 and its corresponding PCT patentapplication Ser. No. PCT/US95/14844 filed Nov. 13, 1995 (WO96/15458,published 23 May 96), both by ELDRIDGE, GRUBE, KHANDROS and MATHIEU,disclose a probe card assembly which includes elongate resilient(spring) contact elements mounted to a “space transformer” component. Asused herein, a space transformer is a multilayer interconnectionsubstrate having terminals disposed at a first pitch on a one surfacethereof and having corresponding terminals disposed at a second pitch onan opposite surface thereof, and is used to effect “pitch-spreading”from the first pitch to the second pitch. In use, the free ends (tips)of the elongate spring contact elements make pressure connections withcorresponding terminals on an electronic component being probed (e.g.,tested).

Elongate, Resilient Cantilever-like Contact Element

[0075]FIGS. 1A and 1B illustrate an elongate resilient (spring) contactelement 100 that is suitable for attachment as a free-standing structureto an electronic component including, but not limited to, the spacetransformer of the aforementioned probe card assembly.

[0076] The structure 100 is elongate, has two ends 102 and 104, acentral portion 106 therebetween, and has an overall longitudinal lengthof “L” between the two ends. The length “L” is in the range of 10-1000mils, such as 40-500 mils or 40-250 mils, preferably 60-100 mils. Aswill become apparent from the discussion that follows, in use thestructure has an effective length of “L1”, less than “L”, which is thelength over which the structure can flex in response to a force appliedthereto.

[0077] The end 102 is a “base” whereat the contact element 100 will bemounted to an electronic component (not shown). The end 104 is a“free-end” (tip) which will effect a pressure connection with anotherelectronic component (e.g., a device-under-test, not shown). Althoughnot illustrated, it is also possible that the contact element 100 has anelongate “tail” portion extending beyond the base end 102, opposite thecentral portion 106.

[0078] The structure 100 has an overall height of “H”. The height “H” isin the range of 4-40 mils, preferably 5-12 mils. (1 mil=0.001 inches)

[0079] As best viewed in FIG. 1A, the structure is “stepped”. The baseportion 102 is at a first height, the tip 104 is at another height, anda middle (central) portion 106 is at a third height which is between thefirst and second heights. Therefore, the structure 100 has two“standoff” heights, labelled “d1” and “d2” in the figure. In otherwords, the spring contact element 100 has two “steps”, a step up fromthe contact end 104 to the central body portion 106, and a further stepup from the central body portion 106 to the base end 102.

[0080] In use, the standoff height “d1”, which is the “vertical” (asviewed in FIG. 1A) distance between the tip 104 and the central portion106, performs the function of preventing bumping of the structure(contact element) with a surface of a component being contacted by thetip end 104.

[0081] In use, the standoff height “d2”, which is the “vertical” (asviewed in FIG. 1A) distance between the base 102 and the central portion106, performs the function of allowing the beam (contact element) tobend through the desired overtravel.

[0082] The dimensions for the standoff heights “d1” and “d2” are:

[0083] “d1” is in the range of 3-15 mils, preferably approximately 7mils+1 mil; and

[0084] “d2” is in the range of 0-15 mils, preferably approximately 7mils+1 mil. In the case of “d2” being 0 mil, the structure would besubstantially planar (without the illustrated step) between the centralportion 106 and the base portion 102.

[0085] As best viewed in FIG. 1B, the structure 100 is preferablyprovided with a “joining feature” 110 at its base portion 102. Thejoining feature may be a tab or, optionally a stud, which is used tofacilitate brazing the probe structure to a substrate (e.g., a spacetransformer or a semiconductor device) during assembly therewith.Alternatively, the component or substrate to which the structure 100 ismounted may be provided with a stud or the like to which the baseportion 102 is mounted.

[0086] In use, the structure 100 is intended to function as a cantileverbeam, and is preferably provided with at least one taper angle, labelled“α” in FIG. 1B. For example, the width “w1” of the structure 100 at itsbase end 102 is in the range of 5-20 mils, preferably 8-12 mils, and thewidth “w2” of the structure 100 at its tip end 104 in the range of 1-10mils, preferably 2-8 mils, and the taper angle “α” is preferably in therange of 2-6 degrees. The narrowing of (taper) the structure 100, fromits base 102 to its tip 104, permits controlled flexure and more evenstress distribution (versus concentration) of the structure 100 when itsbase 102 is secured (immovable) and a force is applied at its tip (104).

[0087] As will be evident in the discussion presented hereinbelow, thewidth of the structure (hence, the taper angle “α”) is readilycontrolled employing well-known lithographic techniques.

[0088] The tip end 104 of the structure 100 is preferably provided withan integral protruding topological feature 108, for example in thegeometric form of a pyramid, to aid in effecting pressure connection toa terminal of an electronic component (not shown).

[0089] As illustrated in FIGS. 1A and 1B, the spring contact element 100is three-dimensional, extending in the x- y- and z-axes. Its length “L”is along the y-axis, its widths (“w1” and “w2”) is along the x-axis, andits thicknesses (“t1” and “t2”) and height (“H”) are along the x-axis.As will become evident in the discussion set forth hereinbelow (see,e.g., FIG. 4B), when the spring contact element 100 is mounted to anelectronic component, it is mounted thereto so that the length and widthof the spring contact element are parallel to the surface of theelectronic component, and its height is normal to the surface of theelectronic component.

[0090]FIG. 1C illustrates a contact structure 150 similar in mostrespects to the structure 100 of FIGS. 1A and 1B. The structure iselongate, has a base end 152 (compare 102) and a tip end 154 (compare104), and a topological feature 158 (compare 108) incorporated into itstip end. The principal difference being illustrated in FIG. 1C is thatthe structure can be provided with a second taper angle “β”.

[0091] As best viewed in FIG. 1C, the thickness “t1” of the structure100 at its base end 102 is in the range of 1-10 mils, preferably 2-5mils, and the thickness “t2” of the structure 100 at its tip end 104 inthe range of 1-10 mils, preferably 1-5 mils, and the taper angle “β” ispreferably in the range of 2-6 degrees.

[0092] The angle “β” (FIG. 1C) may be created using various methods forcontrolling the thickness distribution. For example, if the structure100 is formed by plating, a suitable plating shield can be incorporatedinto the bath. If the structure 100 is formed other than by plating,appropriate known processes for controlling the spatial distribution ofthickness of the resulting structure would be employed. For example,sandblasting or electro-discharge machining (EDM) the structure 100.

[0093] Thus, the structure suitably has a composite (dual) taper fromits base end 102 to its tip end 104. It has a taper angle “α” which, aswill be evident from the description of a contact structure mounted to acomponent or substrate set forth hereinbelow, is parallel to the x-yplane of the substrate or component to which the contact structure 100is mounted. And it has a has a taper angle “β” which represents anarrowing of the structure's cross section (z-axis).

[0094] It is within the scope of this invention that the structure isnot tapered in width, in which case the taper angle “α” would be ZERO.It is also within the scope of this invention that the taper angle “α”is greater than 2-6 degrees, for example as much as 30 degrees. It iswithin the scope of this invention that the structure is not tapered inthickness, in which case the taper angle “β” would be ZERO. It is alsowithin the scope of this invention that the taper angle “β” is greaterthan 2-6 degrees, for example as much as 30 degrees. It is within thescope of this invention that the structure (contact element) is taperedonly in thickness and not in width, or only in width and not inthickness.

[0095] It is within the scope of this invention that the contact elementis tapered to be wider and/or thicker at its contact end 104 than at itsbase end 102, rather than narrower and/or thinner as described above. Itis also possible that the contact element is provided with a pluralityof different tapers, for example, tapering in (e.g., wider to narrower)from the base end to the central portion, then tapering back out (e.g.,narrow to wider) towards the contact end.

[0096] The contact structures 100 and 150 are principally, preferablyentirely, metallic, and may be formed (fabricated) as multilayerstructures, as is described in greater detail hereinbelow.

[0097] Suitable materials for the one or more layers of the contactstructures include but are not limited to:

[0098] nickel, and its alloys;

[0099] copper, cobalt, iron, and their alloys;

[0100] gold (especially hard gold) and silver, both of which exhibitexcellent current-carrying capabilities and good contact resistivitycharacteristics;

[0101] elements of the platinum group;

[0102] noble metals;

[0103] semi-noble metals and their alloys, particularly elements of thepalladium group and their alloys; and

[0104] tungsten, molybdenum and other refractory metals and theiralloys.

[0105] In cases where a solder-like finish is desired, tin, lead,bismuth, indium and their alloys can also be used.

[0106]FIG. 1D shows an enlarged view of the contact end 154 of thecontact structure 150 (equally applicable to the contact ends of othercontact structures illustrated herein). In this enlarged view it can beseen that the contact feature 154 is suitably quite prominent,projecting a distance “d3”, in the range of 0.25-5 mils, preferably 3mils from the bottom (as viewed) surface of the contact end of thespring contact element, and is suitably in the geometric shape of apyramid, a truncated pyramid, a wedge, a hemisphere, or the like.

[0107] The resulting spring contact element has an overall height “H”which is the sum of “d1”, “d2” (and “d3”) plus the thickness of thecentral body portion.

[0108] There has thus been described a exemplary spring contact elementsuitable for effecting connections between two electronic components,typically being mounted by its base end to a one of the two electroniccomponents and effecting a pressure connection with its contact end toan other of the two electronic components, having the followingdimensions (in mils, unless otherwise specified): dimension rangepreferred L  10-1000  60-100 H 4-40  5-12 d1 3-15 7 ± 1 d2 0-15 7 ± 1 d30.25-5    3 w1 3-20  8-12 w2 1-10 2-8 t1 1-10 2-5 t2 1-10 1-5 α  0-30° 2-6° β  0-30°  0-6°

[0109] from which the following general relationships are evident:

[0110] “L” is approximately at least 5 times “H”;

[0111] “d1” is a small fraction of “H”, such as between one-fifth andone-half the size of “H”;

[0112] “w2” is approximately one-half the size of “w1”, and is a smallfraction of “H”, such as between one-tenth and one-half the size of “H”;and

[0113] “t2” is approximately one-half the size of “t1”, such as betweenone-tenth and one-half the size of “H”.

[0114] Another dimension is of interest—namely, the width and length(i.e., footprint) of the overall tip end (104). In instances where thetip end is expected to make contact with a terminal of an electroniccomponent which is recessed (e.g., a bond pad of a semiconductor devicewhich has passivation material surrounding the bond pad), it may bedesirable to ensure that the footprint of the tip end is sufficientlysmall to make such contact. For example, less than 4 mils by 4 mils).Else, it must be ensured that the contact feature (108) is of sufficientheight (d3) to make contact with the recessed terminal. Generallyspeaking, the selection of an appropriate tip end design will bedictated by the peculiarities of the given application. For example, forcontacting bond pads on silicon devices, the tip end design illustratedin FIG. 1D would likely be most appropriate. For contacting C4 bumps,the tip end design illustrated in FIG. 1E (described hereinbelow) wouldlikely be most appropriate.

[0115]FIG. 1E illustrates an alternate embodiment of the inventionwherein discrete contact tip structures 168, such as are described inthe aforementioned PCT/US96/08107 can be mounted to the contact endportions 164 of the spring contact elements, such as by brazing 170thereto. This provides the possibility of the contact tip structure 168having a different metallurgy, than the spring contact element (150).For example, the metallurgy of the spring contact element (150) issuitably targeted at its mechanical (e.g., resilient, spring)characteristics and its general capability to conduct electricity, whilethe metallurgy of a contact tip structure 168 mounted thereto isappropriately targeted to making superior electrical connection with aterminal (see, e.g., 420, hereinbelow) of an electronic component (see,e.g., 422, hereinbelow) being contacted and, if needed, can havesuperior wear-resistance.

Fabricating the Contact Structure

[0116] A contact element such as that described hereinabove would bedifficult, to punch out of a foil of spring material and mount in aprecise location on an electronic component such as a space transformer,at the scale (dimensions) described herein.

[0117] According to an aspect of the invention, processes such asphotolithography are employed to fabricate the spring contact elementsof the present invention with tolerances, both of the springs themselvesand with regard to the relative locations of a plurality of springs,suitable for use as interconnections in the context of fine-pitchmicroelectronics.

[0118] FIGS. 2A-2J illustrates an exemplary process 200 for fabricatingthe aforementioned resilient contact structures 100 (150). The presentinvention is not limited to this exemplary process.

[0119] As illustrated in FIG. 2A, commencing with a suitable sacrificialsubstrate 202, such as a silicon wafer, a blanket layer 204 of siliconnitride (“nitride”) is applied to the surface of the sacrificialsubstrate. This layer 204 will act as an etch stop in subsequent stepsof the process. A layer 206 of a masking material, such as photoresist,is applied over the nitride layer 204, and is imaged and developed usingconventional photolithographic techniques (e.g., actinic light passingthrough a mask).

[0120] It is within the scope of this invention that the sacrificialsubstrate is a material selected from the group consisting of silicon,aluminum, copper, ceramic, and the like. For example, silicon in theform of a silicon semiconductor wafer. Or aluminum or copper in the formof a foil or sheet. Or, aluminum or copper in the form of a layer onanother substrate. The sacrificial substrate can also be a “clad”(multilayer) structure, such as copper-invar-copper oraluminum-alumina-aluminum, and preferably has a coefficient of thermalexpansion which matches that of the component to which the contactstructures are ultimately mounted. The example set forth herein,vis-a-vis the “machining” of the sacrificial substrate is applicable tosacrificial substrates which are silicon. One of ordinary skill in theart to which the present invention most nearly pertains will readilyunderstand how to achieve comparable results with sacrificial substratesformed of other (than silicon) materials. It is within the scope of thisinvention that the sacrificial substrate can be formed oftitanium-tungsten which is readily etched with hydrogen peroxide.

[0121] Using conventional chemical etching techniques, an opening 210 tothe surface of the sacrificial substrate 202 can be created through bothof the layers 206 and 204, as illustrated in FIG. 2C. In the area of theopening 210, the surface of the sacrificial substrate is exposed. Thesurface of the sacrificial substrate is covered by the residual(remaining) portions 204 a and 206 a of the layers 204, 206,respectively, that are not removed by etching.

[0122] Alternatively, as illustrated in FIG. 2B, selected portions ofthe photoresist 206 can be removed employing other techniques, such asknown techniques involving lasers, E-beam, and the like, and theresulting exposed (no longer covered) portions of the nitride layer 204can be removed using chemical etching processes, the result of which isthat an opening 210 to the surface of the sacrificial substrate 202 canbe created, as illustrated in FIG. 2C. Using a laser to remove portionsof the masking layer 206 (other portions 206 a being remaining portions)provides the possibility of having more carefully-controlled aspectratios for the resulting openings 210, for example, obtaining steeperand deeper, more-vertical sidewalls in the opening.

[0123] In a next step of the process 200, illustrated in FIG. 2D, thesacrificial substrate 202 is etched in the openings 210 through thenitride layer 204, using known chemistry for selectively etching thesubstrate. For example, a silicon substrate can selectively be etched(with respect to nitride) using potassium hydroxide (KOH). This willcreate a trench 220 in the substrate 202, the depth of which iscontrolled to correspond to the aforementioned standoff height “d2” (seeFIG. 1A) . Also, in the case of employing a silicon wafer as thesubstrate 202, the sidewall 222 of the trench will favorably exhibit anon-vertical angle “θ”, such as 54.74° (rather than 90°), as may beinherent in and controlled by the crystalline structure of thesubstrate. For example, a silicon substrate having a (100) crystalorientation when etched will etch in the (111) planes.

[0124] After creating the trench 220, the residual portion 204 a of theetch stop layer 204 is preferably removed.

[0125] In a next step of the process 200, illustrated in FIG. 2E, theprevious steps illustrated and described with respect to FIGS. 2A-2D arerepeated, to create another trench 230 in the sacrificial substrate 202that is longitudinally offset from and contiguous with the trench 220.Alternatively, the trench 230 can be formed in an end portion (righthand side, as viewed) of the previously-formed trench 220. In otherwords, an etch stop layer 224 (compare 204) is applied, a masking layer(not shown, compare 206) is applied over the etch stop layer, an openingis created through the masking layer and the etch stop layer, and thesubstrate is etched. This will result in a trench 230 in the substrate202, the depth of which is controlled to correspond to theaforementioned standoff height “d1” (see FIG. 1A). Also, as mentionedhereinabove, in the case of employing a silicon wafer as the substrate202, the sidewall 232 of the trench 230 will favorably be “angled”,rather than vertical.

[0126] In a next step of the process 200, illustrated in FIG. 2F, theprevious steps illustrated and described with respect to FIGS. 2A-2D arerepeated, to create a small geometric intrusion (depression) 240(compare “d3” of FIG. 1D) in the sacrificial substrate 202 in the bottomof the second trench 230. (The term “intrusion” is selected as being thecomplement to “negative of” the resulting protruding feature (108) thatwill be fabricated on the resulting spring contact element. The feature240 could also be considered to be a “depression”, a “recess”, an“indentation” or an “intaglio”.) Namely, an etch stop layer 234 (compare204, 224) is applied, a masking layer (not shown, compare 206) isapplied over the etch stop layer, a small opening is created through themasking layer and the etch stop layer, and the substrate is etched. Theshape of the intrusion 240 is suitably that of an inverted (as viewed)pyramid and, as mentioned hereinabove, may suitably have sides at thecrystalline angle of silicon. As will be evident from the descriptionhereinbelow, this intrusion 240 will define the topological feature 108present on the tip of the contact structure 100 described hereinabove(pyramid, truncated pyramid, etc.). Finally, the nitride layer 234 isremoved.

[0127] Each of the trenches 220 and 230 can be considered to be a“subtrench” of a larger overall trench which also includes thedepression 240.

[0128] The steps described in FIGS. 2A-2F describe the preparation of asacrificial substrate for the fabrication of resilient contactstructures thereon. It is within the scope of this invention thatcertain of the steps described hereinabove could be performed in otherthan the recited order. For example, the trench 230 could be formedprior to forming the trench 220.

[0129] It bears mention here that it is within the scope of thisinvention that the process described hereinabove could be carried out ona silicon wafer that has active devices already formed therein. However,as is evident, the forming of trenches (220 and 230) and features (240)could well destroy the active devices unless (i) they were to be formedat areas of the wafer that do not contain active devices, or (ii) thespring contact elements were fabricated on a sacrificial substrate thenattached to active devices (see e.g., FIGS. 4A-4B hereinbelow), or (iii)a layer of material suitable for performing the function of thesacrificial substrate (202) described hereinabove is first applied tothe surface of the wafer.

[0130] As described hereinabove, the sacrificial substrate has beenprepared with a first trench 220 which is lower than (extends into) thesurface of the substrate, a second trench 230 which is lower than(extends deeper into) and is contiguous (end-to-end) with the firsttrench 220, and an intrusion (negative projection, depression) 240within the second trench 230 which extends yet deeper into thesubstrate. Contact elements will be fabricated in these trenches, thenwill need to be “released” from the trenches.

[0131] In a next step of the process 200, illustrated in FIG. 2G, one ormore metallic layers are blanket deposited, such as by sputtering, ontothe substrate 202. For example, a layer 252 of aluminum followed by alayer 254 of copper. Exemplary thicknesses for these layers are:

[0132] 5000-50,000 Å, preferably 20,000 Å for the first layer 252; and

[0133] 1000-50,000 Å, preferably 5,000 Å for the second layer 254.

[0134] The purposes of these layers 252 and 254 are generally:

[0135] the first layer 252 is a material (such as aluminum) selected forits eventual use as a “release” layer (described hereinbelow); and

[0136] the second layer 254 serves as a “seed” layer for deposition of asubsequent layer (256, described hereinbelow) and, in the case of aprevious aluminum layer 252, will prevent the subsequent layer 256 from“smutting” as a result of removing the previous “release” layer 252.This layer may be removed from the final spring contact element and mayact as a protective “capping” layer during the release process.

[0137] Together, the layers 252 and 254 constitute a “release mechanism”which is incorporated into the sacrificial substrate which, in use,permits the sacrificial substrate to be removed after the spring contactelements fabricated thereon (as described hereinbelow) are mounted tothe terminals of the electronic component.

[0138] Metallic materials forming the resulting contact structures (100,150) can be deposited into the trenches and features formed therein byany suitable technique including, but not limited to: various processesinvolving deposition of materials out of aqueous solutions; electrolyticplating; electroless plating; chemical vapor deposition (CVD); physicalvapor deposition (PVD); processes causing the deposition of materialsthrough induced disintegration of liquid or solid precursors; and thelike, all of these techniques for depositing materials being generallywell known. Electroplating is a generally preferred technique.

[0139] Next, as illustrated in FIG. 2H, a masking layer 258 (compare206), such as photoresist, is applied to the substrate and is patternedto have an openings 260 corresponding to the length “L” and width (“w1”and “w2”, and widths therebetween) of the desired resulting springcontact element (see FIGS. 1A and 1B). A relatively thick “structural”metallic layer 256 is deposited within the openings 260, using anysuitable process such as electroplating of a suitable material such asnickel, atop the previously applied layers 252 and 254. This layer 256is intended to control (dominate) the mechanical characteristics of theresulting spring contact element (100). The opening 260 includes thetrench 220, the trench 230, the depression 240 and a portion of thesubstrate 202 which is adjacent and contiguous with the first trench220.

[0140] An exemplary average ((t2+t2)/2) thickness for this layer 256 is1-10 mils, preferably 1-5 mils. Suitable materials for the layer 256,such as nickel and its alloys, have been set forth hereinabove.

[0141] It is within the scope of this invention that additional layersmay be included in the build-up of the contact structure. For example,prior to depositing the layer 256, a layer of a material selected forits superior electrical characteristics of electrical conductivity, lowcontact resistance, solderability, and resistance to corrosion may bedeposited. For example, gold or rhodium (both of which are excellentcontact materials), nickel-cobalt (a good material for brazing), gold(another good material for brazing), and the like.

[0142] In a next step of the process 200, illustrated in FIG. 2I, themasking layer 258 is removed, exposing the layers 252 and 254. Theselayers are suitably selectively chemically etched, so that all thatremains on the substrate is an elongate structure 270 (compare 100)having a one end 272 (compare 102), an other end 274 (compare 104), acentral portion 276 (compare 106) and a raised topological feature 278(compare 108) at its end 274. This elongate structure 270 is theresulting spring contact element.

[0143]FIG. 2J is another cross-sectional view of the resulting structure270, still resident upon the substrate, with the layers 252 and 254omitted, for illustrative clarity. The similarity between this structure270 and the spring contact element 100 of FIG. 1A is readily apparent.

[0144] One having ordinary skill in the art to which the presentinvention most nearly pertains will recognize that the processesdescribed hereinabove can readily be performed at a plurality oflocations on a sacrificial substrate to result in a plurality of contactstructures (270) having been fabricated at a plurality ofprecisely-controlled predetermined locations on the substrate 202. Theprocess has been described with respect to one exemplary structure 270being fabricated at one location, for purposes of illustrative clarity.

[0145] It is within the scope of this invention that rather thanpatterning a sacrificial substrate to have a plurality of trenches, eachcorresponding to a single resulting contact element, that a sacrificialsubstrate can be prepared with a single very wide set of trenches, (220,230, 240) , then deposit the metals (252, 254, 256), then perform anadditional final masking and etching step to define the individualcontact elements. Such a process would look similar to the processdescribed hereinabove with respect to FIGS. 2A-2G, followed by blanketdeposition of the metal (256) layers, followed by masking and etching todefine the individual contact elements.

An Alternate Embodiment

[0146]FIGS. 3A and 3B illustrate another one of many possibleembodiments for a contact structure 300 fabricated by the techniquesdescribed hereinabove. Instead of a flat connection tab (see 110), asomewhat truncated-pyramidal joining feature (stud) 310 is fabricated asan attachment feature at the base portion 304 of the contact structure300. When the contact structure 300 is mounted to a substrate, such as aspace transformer, this stud 310 will allow for some misalignmenttolerance during assembly. The remaining portions of the contactstructure 300 are comparable to those described hereinabove with respectto the contact structure 270 —namely, a central main body portion 306(compare 276), a contact end portion 304 (compare 274), and a feature308 (compare 278).

[0147] Thus, there has thus been shown an exemplary process forfabricating elongate resilient (spring) interconnection (contact)elements on a sacrificial substrate. This can be considered to be an“interim” product, awaiting further use, as follows:

[0148] Alternative A: These spring contact elements can simply beremoved from the sacrificial substrate, resulting in a “bucket ofsprings” which may be attached, such as with automated equipment, to anelectronic component, although the benefit of having lithographically(i.e., to very close tolerances) located the plurality of spring contactelements with respect to one another would be lost.

[0149] Alternative B: A more “viable” technique for installing thespring contact elements onto an electronic component, involving removingthe sacrificial substrate after the contact structures resident thereonare mounted (by the base ends) to an electronic component or to asubstrate, is described hereinbelow with respect to FIGS. 4A-4C.

Removing the Sacrificial Substrate

[0150] With regard to either of the alternatives (“A” or “B”, set forthhereinabove, a suitable mechanism must be employed for removing thesacrificial substrate (i.e, releasing the fabricating contact elementsfrom the sacrificial substrate whereupon they reside). Exemplarysuitable mechanisms include, but are not limited to:

[0151] chemically etching to release the contact structures (e.g., 270)from the sacrificial substrate (202). As mentioned above, the aluminumlayer 252 is readily selectively etched to cause separation of thecontact structure 270 from the substrate 202. (The copper layer 254helps prevent contamination of the layer 256 in such a process, and mayultimately be etched from the separated contact structure 270.)

[0152] in lieu of the aluminum and copper layers described hereinabove,employing layers of materials that are non-wetting with respect to oneanother and/or that ball up when heated (e.g., lead, indium, tin), thenheating the substrate 202 to cause the contact structures 270 to bereleased therefrom.

Mounting the Contacts to a Substrate

[0153] As mentioned hereinabove, a plurality of contact structures(e.g., 270) fabricated upon a sacrificial substrate (e.g., 202) can bemounted (affixed) to another substrate or to an electronic componentsuch as a space transformer.

[0154]FIG. 4A illustrates a technique 400 wherein a plurality (two ofmany shown) of contact structures 402 (compare 100, 150, 270, 300) havebeen fabricated on a sacrificial substrate 404 (compare 202). The baseend portions (compare 310) of the contact structures 402 are broughtinto contact with a corresponding plurality of terminals 406 on anelectronic component 408 such as the aforementioned space transformer ofa probe card assembly, whereupon the base end portions are suitablysoldered or brazed 410 to the terminals 406.

[0155] It is within the scope of this invention that any suitabletechnique and/or material for affixing the base end portions of thecontact structures (402) to terminals of an electronic component beemployed, including brazing, welding (e.g., spot welding), soldering,conductive epoxy, tacking the contact structure in any suitable mannerto the terminal and securely affixing the contact structure to theterminal by plating (e.g., electroplating), and the like.

[0156] The sacrificial substrate 404 is now removed, in any suitablemanner such as those described hereinabove (e.g., chemical etching,heating), resulting in an electronic component (408) having springcontact elements (402) affixed thereto, as illustrated in FIG. 4B.

[0157] As is evident in FIG. 4B, a plurality of elongate spring contactelements can be mounted to an electronic component having a plurality ofterminals on a surface thereof. Each spring contact element has a baseend and a contact end opposite the base end, and is mounted by its baseend to a corresponding terminal of the electronic component. The contactend of each spring contact element extends above the surface of theelectronic component to a position which is laterally offset from itsbase end.

[0158] As mentioned hereinabove, when mounted, the contact structure 402(compare 100) has an “effective” length of “L1”, this being the lengthbetween the tip feature (compare 108) and the inwardmost positionwhereat the base end (compare 102) is affixed to the component 408. The“effective” length represents the length over which the contactstructure can deflect in response to compressive forces applied at thetip end thereof (e.g., at the tip feature).

[0159]FIG. 4C illustrates an application for the spring contact elements(resilient contact structures) of the present invention wherein thespring contact elements have been mounted in the manner described withrespect to FIG. 4B to a space transformer component (408) of a probecard assembly (not shown) so that the contact features (compare 308) attheir contact ends (compare 304) make pressure connections withterminals 422 of an electronic component 420 such as a semiconductordevice, or an area of a semiconductor wafer (not shown) containing aplurality of semiconductor devices. As described hereinabove, withrespect to FIG. 1E, it is within the scope of this invention thatseparate and discrete contact tip structures (168) be affixed to thecontact end portions of the spring contact element.

[0160] It is within the scope of this invention that the substrate(component) to which the structures 402 are mounted, for example thecomponent 408 illustrated in FIG. 4C are active components, such asASICs.

[0161] It is also within the scope of the invention, as is illustratedin FIG. 4C, that the component or substrate to which the structures(e.g., 402) are mounted can be provided with a contiguous (asillustrated) or segmented ground plane to control impedance. Such aground plane may comprise a plurality of ground lines 412 aligneddirectly underneath the structures 402, but sufficient clearance for thetip of the structure to deflect must be assured. Alternatively, theground plane 412 can be covered with an insulating layer. Anotherapproach would be to dispose ground plane lines 414 on the surface ofthe substrate 408 slightly (such as 1 mil, in the x-axis) offset fromdirectly underneath the structures 402, and laying parallel to thestructure.

[0162]FIG. 4D illustrates an alternate embodiment 440 of the presentinvention wherein a cavity (trench) 442 is been formed in the surface ofthe substrate or component 444 (compare 408) to which the contactstructures 450 (compare 402) have been mounted. The trench 442 islocated so that it is underneath at least the contact end portion 454(compare 104) of the contact structure, and preferably extendsunderneath a substantial portion of the contiguous central body portion456 (compare 106) of the spring contact element. The trench extends of adepth “d4” within the substrate 444 a suitable distance to allow for agreater range of deflection of the contact end portion 454 when, in use,it is urged against an electronic component (see, e.g., FIG. 4C). InFIG. 4D, one trench 442 is illustrated extending under a plurality (twoof many shown) spring contact elements. It is within the scope of thisinvention that there is a single discrete trench under each of theplurality of spring contact elements (450) structures mounted to anelectronic component (444).

[0163]FIG. 4E illustrates an alternate embodiment of the presentinvention wherein a spring contact element 460 is mounted to anelectronic component 470 (compare 444) via a stud 472 extending from asurface of the electronic component 470. The base end 462 of the springcontact element 460 is suitably brazed to the stud 472. The stud 472suitably has a height in the range of 3-4 mils.

[0164]FIG. 4E also illustrates an alternate embodiment of the presentinvention wherein the spring contact element 460 is formed with but asingle step or offset (rather than two steps). As illustrated herein,the offset of the base end portion 462 from the central body portion 466(compare “d2” in FIG. 1A) is ZERO. In other words, in this example, thebase end portion 462 is coplanar with the central body portion 466.Since there is no offset at the base end portion, the base end 462 ismounted to a stud 472 on the surface of the electronic component 470 sothat the body portion 466 is elevated above the surface of the component470. The contact end portion 464 (compare 104) preferably remains offsetby a distance “d1” from the central body portion 466. As suggested bythis figure, many of the variations (alternate embodiments) of thepresent invention can be combined (mixed and matched) to arrive at adesired arrangement of spring contact elements affixed to an electroniccomponent.

[0165]FIG. 4F illustrates another embodiment of the invention whereinthe spring contact element (contact structure) 480 is formed without anystep or offset (rather than one or two steps). As in the previousexample, the offset of the base end portion 482 from the central bodyportion 486 (compare “d2” in FIG. 1A) is ZERO, and the base end portion482 is coplanar with the central body portion 486. Since there is nooffset at the base end portion, the base end 482 is mounted to a stud492 on the surface of the electronic component 490 so that the bodyportion 486 is elevated above the surface of the component 490. Also,the offset of the contact end portion 484 (compare 104) from the centralbody portion 486 (compare “d1” in FIG. 1A) is ZERO, and the contact endportion 484 is coplanar with the central body portion 486. Since thereis no offset at the contact end portion, a prefabricated contact tipstructure 488 (compare 168) may be affixed (e.g., joined, such as bybrazing) to the contact end 484 so that the body portion 486 will bespaced away from a component (not shown, compare 420) being contacted bythe contact structure 480.

Probe Applications

[0166]FIG. 5 illustrates an application wherein a plurality of springcontact elements 500 such as those described hereinabove are arranged ona substrate such as a space transformer, and affixed thereto in themanner described hereinabove, so that their contact ends are disposed ina manner suitable for making contact with the bond pads of asemiconductor device having its bond pads arranged along its periphery.

[0167] Each contact element 500 (compare 100) has a base end 502(compare 102) and a contact end 504 (compare 104), and are mounted to anelectronic component such as a space transformer component(schematically illustrated by the dashed line 510) of a probe cardassembly. The contact ends 504 are arranged close to one another, in apattern mirroring that of the bond pads 522 (illustrated schematicallyby circles) of an electronic component (schematically illustrated by thedashed line 520) such as a semiconductor device. The spring contactelements 500 “fan-out” from their contact ends 504, so that their baseends 502 are disposed at a greater pitch (spacing from one another) thantheir contact ends 504.

[0168]FIG. 6 illustrates another application wherein a plurality ofspring contact elements 600 such as those described hereinabove arearranged on a substrate such as a space transformer, and affixed theretoin the manner described hereinabove, so that their contact ends aredisposed in a manner suitable for making contact with the bond pads of asemiconductor device having its bond pads arranged in a row along acenterline thereof.

[0169] Each spring contact element (compare 100), generally denoted bythe reference numeral 600, has a base end 602 (compare 102) and acontact end 604 (compare 104), and are mounted to an electroniccomponent such as a space transformer component (schematicallyillustrated by the dashed line 610) of a probe card assembly (notshown). The contact ends 604 are arranged close to one another, in apattern mirroring that of the bond pads 622 (illustrated schematicallyby circles) of an electronic component (schematically illustrated by thedashed line 620) such as a semiconductor device. The spring contactelements 600 are arranged in the following sequence:

[0170] a first spring contact element 600 a is relatively short (e.g.,has a length of 60 mils ), and is disposed to extend towards a one side(right, as viewed) of the electronic component 620;

[0171] a second spring contact element 600 b, adjacent the first springcontact element 600 a, is also relatively short (e.g., has a length of60 mils ), and is disposed to extend towards an opposite side (left, asviewed) of the electronic component 620;

[0172] a third spring contact element 600 c, adjacent the second springcontact element 600 b, is relatively long (e.g., has a length of 80 mils), and is disposed to extend towards the one side (right, as viewed) ofthe electronic component 620; and

[0173] a fourth spring contact element 600d, adjacent the third springcontact element 600 c, is also relatively long (e.g., has a length of 80mils ), and is disposed to extend towards the opposite side (left, asviewed) of the electronic component 620. In this manner, the contactends 604 are disposed at a fine-pitch commensurate with that of the bondpads 622, and the base ends 602 are disposed at a significantly greaterpitch from one another.

[0174] The showing of only two different-length contact structures ismerely exemplary and it should be understood that it is within the scopeof this invention that a plurality of spring contact elements havingmore than two different lengths can be disposed on a common substrate.The showing of only two different-length contact structures is merelyexemplary.

[0175] It is within the scope of this invention that the techniquesillustrated in FIGS. 5 and 6 may be used to generate a plurality ofprobes (spring contact elements) in any arrangement required for probingof either peripheral or lead-on-center (LOC) devices.

Additional Features and Embodiments

[0176] In cases where there are a plurality of spring contact elementsmounted to a substrate and they are of different lengths (see, e.g.,FIG. 6), and assuming that the cross-sections and metallurgy of thespring contact elements are the same as one another, the differentlength spring contact elements will evidently exhibit different reactiveforces (spring constants, k)

[0177] It is therefore within the scope of this invention that thespring constants of a plurality of spring elements exhibiting differentspring constants can be adjusted (tailored), on an individual basis, tomake them more uniform with one another.

[0178]FIG. 7A illustrates a technique for tailoring spring constant. Inthis example, a spring contact element 700 (compare 450) is mounted byits base end 702 (compare 452) to an electronic component 710 (compare444). A trench 712 (compare 442) is formed in the surface of theelectronic component 710 and extends from under the contact end 704(compare 454) of the spring contact structure 700, along the bodyportion 706 (compare 456) thereof, towards the base end 702 of thespring contact element 700 to a position (point) “P” which is located aprescribed, fixed distance, such as 60 mils from the contact end 704.When a force is applied downwards to the contact end 704, the entirespring contact element 700 will bend (deflect) until the body portion706 contacts the end of the trench 712 at the point “P”, whereupon onlythe outermost portion (from the point “P” to the end 704) of the springcontact element is permitted to deflect. The outermost portion of thespring contact element has an ‘effective’ length of “L1”. The outermostportion of the spring contact element has an ‘effective’ length of “L1”.In this manner, the reaction to applied contact forces can be madeuniform among spring contact elements of various lengths (so long as thepoint “P” falls somewhere within the central body portion of the springcontact element).

[0179]FIG. 7B illustrates another technique for tailoring springconstant. In this example, a spring contact element 720 (compare 450) ismounted by its base end 702 (compare 452) to an electronic component 710(compare 444). A structure 732 (compare 712) is formed on the surface ofthe electronic component 730 (compare 710) at a location between thebase end 722 of the spring contact structure 720, between the surface ofthe electronic component 730 and the central body portion 726 (compare706) of the spring contact element 720 and extends along the bodyportion 726 (compare 706) thereof, towards the contact end 724 of thespring contact element 720 to a position (point) “P” which is located aprescribed, fixed distance, such as the aforementioned (with respect toFIG. 7A prescribed distance, from the contact end 724. The structure issuitably a bead of any hard material, such as glass or a pre-cut ceramicring, disposed on the surface of the electronic component 730. When aforce is applied downwards to the contact end 724, only the outermostportion (from the point “P” to the end 724) of the spring contactelement is permitted to deflect. As in the previous embodiment, thereactions to applied contact forces can be made uniform among springcontact elements of various lengths.

[0180]FIG. 7C illustrates yet another technique for tailoring springconstant. In this example, a spring contact element 740 (compare 720) ismounted by its base end 742 (compare 722) to an electronic component 750(compare 730). An encapsulating structure 752 (compare 732) is formed onthe surface of the electronic component 750 in a manner similar to thestructure 732 of the previous embodiment. However, in this case, thestructure 752 fully encapsulates the base end 742 of the spring contactstructure 740 and extends along the body portion 746 (compare 726)thereof, towards the contact end 744 thereof, to a position (point) “P”which is located a prescribed, fixed distance, such as theaforementioned (with respect to FIG. 7B prescribed distance, from thecontact end 744. The outermost portion of the spring contact element hasan ‘effective’ length of “L1”. As in the previous embodiment, when aforce is applied downwards to the contact end 744, only the outermostportion (from the point “P” to the end 744) of the spring contactelement is permitted to deflect. As in the previous embodiment, thereactions to applied contact forces can be made uniform among springcontact elements of various lengths.

[0181]FIG. 7D illustrates yet another technique for tailoring springconstant. In this example, a spring contact element 760 (compare 740) ismounted by its base end 762 (compare 742) to an electronic component 770(compare 750). In this example, the body portion 766 is formed with a“kink” 772 at a position (point) “P” which is located a prescribed,fixed distance, such as the aforementioned (with respect to FIG. 7Cprescribed distance, from the contact end 764. The outermost portion ofthe spring contact element has an ‘effective’ length of “L1”. As in theprevious embodiment, when a force is applied downwards to the contactend 744, only the outermost portion (from the point “P” to the end 744)of the spring contact element is permitted to deflect. (The kink 772 canbe sized and shaped so that the entire contact structure deflectsslightly before the kink 772 contacts the surface of the component 770,after which only the outermost portion of the spring element willcontinue to deflect.) As in the previous embodiment, the reactions toapplied contact forces can be made uniform among spring contact elementsof various lengths.

[0182] It is within the scope of this invention that other techniquescan be employed to “uniformize” the spring constants among contactelements having different overall lengths (“L”) . For example, theirwidths and or “α” taper can be different from one another to achievethis desired result.

Alternate Embodiment

[0183] The spring contact elements illustrated and described hereinabovehave been elongate and linear (disposed along the y-axis), generallybest suited to accommodate movement (deflection) in the z-axis (i.e.,normal to the component or substrate to which they are mounted).

[0184] It is within the scope of this invention that additional“dimensionality” and commensurate additional freedom of movement beincorporated into the resulting spring contact element.

[0185]FIG. 8A illustrates a spring contact element 800 that has beenfabricated according to the techniques set forth hereinabove, with theexception (noticeable difference) that the central body portion 806(compare 106) of the contact element is not straight, Although it maystill lay in a plane (e.g., the x-y plane), it is illustrated as joggingalong the x-axis while traversing the y-axis, in which case the base end802 (compare 102) will have a different x-coordinate than the contactend 804 (compare 104) or the contact feature 808 (compare 108) disposedat the contact end 804.

[0186]FIG. 8B illustrates a spring contact element 850 that is similarin many respects to the spring contact element 800 of FIG. 8A, with theexception that there is a step between the central body portion 856(compare 806) and the base portion 852 (compare 802) in addition to thestep between the central portion 856 and the contact end portion 854(compare 804). The contact element 850 is illustrated with a contactfeature 858 (compare 808) at its contact end 854.

Controlled Impedance

[0187] For use in probing semiconductor devices, particularly at speedtesting, it is advantageous that the spring contact element havecontrolled impedance.

[0188] FIGS. 9A-9C illustrate a technique 900 for achieving controlledimpedance in a spring contact element, according to the invention.

[0189] In a first step, best viewed in FIG. 9A, a spring contact element900 (compare 700) is mounted by its base end 902 (compare 702) to aterminal 912 of an electronic component 910 (compare 710) such as aspace transformer component of a probe card assembly. The contact tipend 904 (compare 704) is elevated above the surface of the component9140 and is illustrated as having a contact feature. The spring contactstructure has a central body portion 906 (compare 706) between its baseand tip ends.

[0190] In a next step, best viewed in FIG. 9B, the tip end 904 of thespring contact element is masked (not shown) , and a suitable thin(e.g., 1-10 μm)insulating layer 920, such as parylene, is deposited,such as by vapor deposition, onto all but the tip end 904 of the springcontact element, and adjacent surface of the electronic component.

[0191] In a next step, best viewed in FIG. 9B, while the tip end 904 ofthe spring contact element is still masked (not shown), a suitable thin(e.g., less than 0.25 mm) layer 922 of conductive material, such as anyof the conductive metal material described herein, is deposited, such asby sputtering, onto all but the tip end 904 of the spring contactelement, and adjacent surface of the electronic component. Finally, thetip end 904 is unmasked. This results in the central body portion 906 ofthe spring contact element being enveloped by a conductive layer 922,with an insulating layer 920 therebetween.

[0192] The conductive layer 922 is suitably connected to ground tofunction as a ground plane and control the impedance of the resultingspring contact element. For example, as best viewed in FIG. 9B, thecomponent 910 is provided with a second terminal 914 which is electricalground. This terminal 914 is suitably masked along with the tip end 904of the spring contact element prior to applying the insulating layer920, so that the subsequent conductive layer 922 will also depositthereon and be connected thereto.

[0193] Evidently, this thicknesses of the layers 920 and 922 need onlybe sufficient to be continuous, and to provide the sought aftercontrolled impedance, and should not be so thick as to interfere withthe mechanical operation of the spring contact element. Therepresentations in FIGS. 9B and 9C are not drawn to scale.

[0194] Although the invention has been illustrated and described indetail in the drawings and foregoing description, the same is to beconsidered as illustrative and not restrictive in character—it beingunderstood that only preferred embodiments have been shown anddescribed, and that all changes and modifications that come within thespirit of the invention are desired to be protected. Undoubtedly, manyother “variations” on the “themes” set forth hereinabove will occur toone having ordinary skill in the art to which the present invention mostnearly pertains, and such variations are intended to be within the scopeof the invention, as disclosed herein.

[0195] For example, the resulting spring contact elements may beheat-treated to enhance their mechanical characteristics, either whilethey are resident upon the sacrificial substrate or after they aremounted to another substrate or an electronic component. Also, any heatincident to mounting (e.g., by brazing) the spring contact elements to acomponent can advantageously be employed to “heat treat” the material ofthe spring contact element.

[0196] For example, a comparable spring contact element could befabricated without etching into the sacrificial substrate, by disposingmultiple layers of photoresist (masking material) onto a substrate,forming openings therein, seeding the opening for electroplating or thelike, building up a metallic mass within the opening, and removing thephotoresist. Such a technique would be particularly well suited tofabricating spring contact elements directly upon active semiconductordevices.

[0197] For example, it is within the scope of this invention that thecontact structure can be fabricated on or attached to activesemiconductor devices.

What is claimed is:
 1. A microelectronic spring contact element, comprising: an elongate member of length “L” having a base end portion, a contact end portion opposite the base end portion, and a central body portion contiguous with each of the base and contact end portions; the contact end portion is offset in a first direction from the central portion by a distance “d1”; the base end portion is offset in a second direction opposite the first direction from the central portion by a distance “d2”; wherein: the base end portion is adapted in use to be mounted to a first electronic component; and the tip end portion is adapted in use to make a pressure connection with a second electronic component.
 2. A microelectronic spring contact element, according to claim 1, wherein: the distance “d1” is in the range of 3-15 mils.
 3. A microelectronic spring contact element, according to claim 2, wherein: the distance “d1” is approximately 7 mils.
 4. A microelectronic spring contact element, according to claim 1, wherein: the distance “d2” is in the range of 0-15 mils.
 5. A microelectronic spring contact element, according to claim 4, wherein: the distance “d2” is approximately 7 mils.
 6. A microelectronic spring contact element, according to claim 1, wherein: the distance “d1” is in the range of 3-15 mils; and the distance “d2” is in the range of 0-15 mils.
 7. A microelectronic spring contact element, according to claim 1, wherein: the spring contact element is thicker at the base end portion than at the contact end portion.
 8. A microelectronic spring contact element, according to claim 1, wherein: a thickness “t1” of the base end portion is in the range of 1-10 mils.
 9. A microelectronic spring contact element, according to claim 8, wherein: the thickness “t1” of the base end portion is in the range of 2-5 mils.
 10. A microelectronic spring contact element, according to claim 1, wherein: a thickness “t2” of the tip end portion is in the range of 1-10 mils.
 11. A microelectronic spring contact element, according to claim 10, wherein: the thickness “t2” of the tip end portion is in the range of 1-5 mils.
 12. A microelectronic spring contact element according to claim 7, wherein: the spring contact element has a thickness taper angle “β” in the range of 0-30 degrees.
 13. A microelectronic spring contact element according to claim 12, wherein: the spring contact element has a thickness taper angle “β” in the range of 0-6 degrees.
 14. A microelectronic spring contact element, according to claim 1, wherein: the spring contact element is wider at the base end portion than at the contact end portion.
 15. A microelectronic spring contact element, according to claim 1, wherein: the width “w1” of the base end portion is in the range of 3-20 mils.
 16. A microelectronic spring contact element, according to claim 15, wherein: the width “w1” of the base end portion is in the range of 8-12 mils.
 17. A microelectronic spring contact element, according to claim 1, wherein: the width “w2” of the tip end portion is in the range of 1-10 mils.
 18. A microelectronic spring contact element, according to claim 17, wherein: the width “w2” of the tip end portion is in the range of 2-8 mils.
 19. A microelectronic spring contact element according to claim 14, wherein: the spring contact element has a widthwise taper angle “α” in the range of 2-6 degrees.
 20. A microelectronic spring contact element, according to claim 1, wherein: the spring contact element is thicker at the base end portion than at the contact end portion; the spring contact element is wider at the base end portion than at the contact end portion; the spring contact element has a thickness taper angle “β” in the range of 0-6 degrees. ; and the spring contact element has a widthwise taper angle “α” in the range of 2-6 degrees.
 21. A microelectronic spring contact element, according to claim 1, wherein: the length “L” is in the range of 10-1000 mils.
 22. A microelectronic spring contact element, according to claim 21, wherein: the length “L” is in the range of 60-100 mils.
 23. A microelectronic spring contact element, according to claim 1, wherein: the elongate member has an overall height “H” which is the sum of “d1”, “d2” and a thickness at the central body portion of the member; and the overall height “H” is in the range of 4-40 mils.
 24. A microelectronic spring contact element, according to claim 23, wherein: the overall height “H” is in the range of 5-12 mils.
 25. A microelectronic spring contact element, according to claim 1, wherein: the elongate member has an overall height “H”, which is the sum of “d1”, “d2” and a thickness at the central body portion of the member; and the length “L” is approximately at least FIVE times the overall height “H”.
 26. A microelectronic spring contact element, according to claim 1, wherein: the elongate member has an overall height “H” which is the sum of “d1”, “d2” and a thickness at the central body portion of the member; and the distance “d1” is between one-fifth and one-half the size of the overall height “H”.
 27. A microelectronic spring contact element, according to claim 1, wherein: the elongate member has an overall height “H” which is the sum of “d1”, “d2” and a thickness at the central body portion of the member; the member has a width “w1” at its base end portion; the member has a width “w2” at its contact end portion; and the width “w2” is between one-tenth and one-half the size of the overall height “H”.
 28. A microelectronic spring contact element, according to claim 1, wherein: the contact end portion is provided with an integral protruding feature.
 29. A microelectronic spring contact element, according to claim 28, wherein: the integral protruding feature is in the form of a pyramid or a truncated pyramid.
 30. A microelectronic spring contact element, according to claim 28, wherein: the integral protruding feature protrudes a distance “d3” from a surface of the contact end portion which is in the range of 0.25-5 mils.
 31. A microelectronic spring contact element, according to claim 30, wherein: the distance “d3” is 3 mils.
 32. A microelectronic spring contact element, according to claim 1, further comprising: a separate and distinct contact tip structure mounted to the contact end portion.
 33. A microelectronic spring contact element, according to claim 32, wherein: the contact tip structure has a different metallurgy than the spring contact element.
 34. An electronic component, comprising: an electronic component having a plurality of terminals on a surface thereof; a plurality of elongate spring contact elements, each having a base end and a contact end opposite the base end, mounted by their base ends to the terminals, their contact ends extending above the surface of the electronic component to positions which are laterally offset from the respective base ends.
 35. An electronic component, according to claim 34, further comprising: cavities formed in the surface of the electronic component extending from underneath the contact end of a corresponding spring contact element towards the base end of the spring contact element, said cavities allowing the contact ends to deflect below the surface of the electronic component.
 36. An electronic component, according to claim 34, further comprising: a rigid material disposed on the surface of the electronic component, said rigid material extending from the base end of a corresponding spring contact element partially along a central body portion of the spring contact element towards the contact end of the spring contact element.
 37. An electronic component, according to claim 34, further comprising: a material encapsulating a portion of the spring contact element including the base end and a contiguous portion of the central body portion thereof, the contact end and a contiguous adjacent remaining portion of the central body portion being free of material encapsulating the spring contact element.
 38. Electronic interconnection apparatus, comprising: a sacrificial substrate; and a plurality of spring contact elements residing upon the sacrificial substrate; wherein, in use, the spring contact elements can be mounted, en masse, to terminals of an electronic component.
 39. Electronic interconnection apparatus, according to claim 38, wherein: the sacrificial substrate is a material that matches the coefficient of thermal expansion of silicon.
 40. Electronic interconnection apparatus, according to claim 38, wherein: the sacrificial substrate is a material selected from the group consisting of silicon, aluminum, copper, ceramic, copper-invar-copper and aluminum-alumina-aluminum.
 41. Electronic interconnection apparatus, according to claim 38, further comprising: a release mechanism incorporated into the sacrificial substrate which, in use, permits the sacrificial substrate to be removed after the spring contact elements are mounted to the terminals of the electronic component.
 42. Method of mounting a plurality of spring contact elements to terminals of an electronic component, comprising: fabricating a plurality of spring contact elements upon a sacrificial substrate; subsequently, while the spring contact elements are resident on the sacrificial substrate, mounting the spring contact elements to terminals of an electronic component; and after the spring contact elements are mounted to the terminals of the electronic component, removing the sacrificial substrate.
 43. Method, according to claim 42 wherein: the electronic component is a space transformer.
 44. A method of making a plurality of spring contact elements which are supported in a predefined spatial relationship with one another, comprising: defining a plurality of trenches in a surface of a sacrificial substrate; depositing at least one layer of a metallic material into the trenches, the metallic material in each trench representing a one of the plurality of spring contact elements; wherein each spring contact element is elongate, and is formed to have a contact end portion that is deeper in the surface of the sacrificial substrate than a central body portion of the contact element, thereby forming a first step between the contact end portion and the central body portion.
 45. A method, according to claim 44, further comprising: each trench comprises at least two contiguous subtrenches formed in the surface of the sacrificial substrate, a first one of the two subtrenches being at a first depth, a second one of the two subtrenches being at a second depth which is deeper than the first depth so that the resulting contact element has at least one step.
 46. A method, according to claim 44, further comprising: prior to depositing the at least one layer of metallic material, forming a depression adjacent an end of the trench.
 47. A method, according to claim 44, further comprising: after making the spring contact elements on the sacrificial substrate, mounting them to an electronic component, then removing the sacrificial substrate.
 48. A method of mounting a plurality of spring contact elements to a microelectronic component, comprising: providing a plurality of elongate spring contact elements, each having a base end, a contact end, and a central body portion therebetween; and mounting the base ends of the spring contact elements to corresponding terminals on an electronic component, the contact ends of the contact elements extending above the surface of the electronic component.
 49. Method, according to claim 48, wherein: the electronic component is a space transformer of a probe card assembly.
 50. Method, according to claim 48, wherein: the electronic component is a semiconductor device.
 51. Method of forming microelectronic spring contact elements on a silicon substrate, comprising: providing a blanket layer of silicon nitride on a surface of a silicon substrate; creating a plurality of openings through the silicon nitride layer, thereby exposing the surface of the silicon substrate; etching the silicon substrate within the openings to form a corresponding plurality of first trenches, each extending to a first depth below the surface of the silicon substrate; masking a portion of the first trenches; etching the silicon substrate within an unmasked portion of the first trenches to form a corresponding plurality of second trenches each extending to a second depth, greater than the first depth, below the surface of the silicon substrate; depositing metallic material into the first and second trenches, the metallic material deposited into each first trench and corresponding second trench serving as one of a plurality of resulting microelectronic spring contact elements.
 52. Method, according to claim 51, further comprising: when depositing the metallic material into the first and second trenches, depositing the metallic material onto a portion of the surface of the silicon substrate which is adjacent to and contiguous with the first trenches.
 53. Method, according to claim 52, further comprising: prior to depositing the metallic material, depositing a release layer into the first and second trenches and contiguous adjacent portion of the silicon substrate, said release layer adapted in use to permit the resulting microelectronic spring contact elements to be removed from the silicon substrate. 